Specific thin-layer chromatographic method for the determination of theophylline in plasma in the presence of some other drugs.

A simple spectrodensitometric method for the direct determination of theophylline was developed from measurement of the absorbance of the compound on silica gel layers irradiated at 275 nm. Auantities as low as 0.010 mug can be detected and a linear relationship was obtained between peak area and the amount of the drug in the spots from 0.025-0.200 mug. The recovery over the usual range of plasma concentration (2.5-20 mug/ml) was 95-107%. The method is sufficiently sensitive and specific for clinical purposes and the time for the assay is about 2 h. Caffeine, frequently present in human plasma, was well separated from theophylline at all concentration levels as were several other drugs commonly used in respiratory problems.